If someone tries to convince you that cloud point of sale is a good idea PLEASE ask yourself three questions...

99.9 % up-time is 8 hours per year of "gone fishing sign on the door" down time. -And that doesn't take into account the slow downs that backup your checkout lanes, frustrate your customers, then cost you money and reputation.

And years later they still cannot solve their cloud problems. 

Back in 2014 Google was making about $658 per SECOND off the internet. It's way more today. Imagine what downtime costs them and what they would do to prevent it if they could.

If you were to search "internet outage" you'd find entire sites dedicated to tracking down times, many have occurred since 2014. Some even suggest games to play while waiting for internet resources to come back up.

Now imagine it's your check out lanes that are down. There is no game in the world that will placate a customer standing across the checkout counter from you, waiting to part with their hard earned money, so they can get home with their purchase.

Google doesn't have a choice, they are an internet company. Their programs and data are kept where their products are, and yours should be too.

To be fair, one of the main reasons Google cannot solve their cloud problems, is because they are out of Google's control, just as they would be out of your control.

-It's been said that success does not stem from doing one big thing right, it stems from not doing lots of little things wrong. If you still think cloud based point of sale is just one little thing, please take heed. 

http://www.valuewalk.com/2017/09/google-netflix-facebook-and-amazon/

Cloud Geek Speak -It's all about the network

Cloud Dependent Systems:

A cloud dependent system has it's data living only "in the cloud". The application (program) may live on your device and/or in the cloud. It really doesn't matter much, because if your data is only in the cloud and you can't get to it you might as well be using a shoe box and a pencil for your point of sale. There are not as many of these around any more, see their cousin, Cloud Primary Hybrids below.

Hybrid Systems:

A hybrid system houses your data and your application in at least two places. There are primarily three kinds of hybrid systems:

Cloud Primary Hybrids are rare, mainly because the way they do things is considered by many to be backwards.
They bet on the up-time of the internet and everything in between, then try to fall back to the local device in a timely fashion during times of trouble. Most of these are the result of Cloud Dependent Systems realizing their design flaws and trying to improve upon them. Cloud primary or dependent systems may be OK for applications that sell services or for accounting systems, where a little delay on every transaction is not an issue, but they are generally not suitable for product in hand point of sale when a customer is waiting.

Device Primary Hybrids take the problems of "cloud primary hybrids" and flip them around.
They use the device as primary and syncing or backing up data to the cloud. This functions better, but you still still suffer when there are bandwidth constraints, especially if you have more than one device because "real-time information",  like knowing current on hand count, would require every transaction to sync to every device (causing exponential network traffic) OR every device must sync to the cloud and cloud based lookups must be performed. While a system like this could be used to enter transactions when the network is down it suffers from three main problems. 1) you could not process credit cards without some other failover, 2) you would not get real-time data (sales, on-hand levels, price updates, etc) from the other terminals and 3) when your store is busy, the internet is busy. That's because people tend to shift gears (go to lunch, get out of work, school, etc) at the same time each day.

Multi-tenant. A true cloud based solution is also usually defined as multi-tenant, this means your data is kept in a database along with other store's data. Think of it as living in an apartment building instead of a house. Each has pros and cons, for both the tennant and the landlord.

LAN Primary Hybrids are the best of both worlds. (Acme is a LAN Primary Hybrid)
These are also sometimes called "on prem" (on premises) solutions, but no other solution is a hybrid quite like Acme. -On Prem design improves upon Device Primary Hybrids in a number of important ways. The application and data are on the device (if you only have one) or on a server device (if you have more than one device) per premises. This solves the real-time problem. Data can be backed up to the cloud, for safekeeping.

Speaking for Acme (other LAN Primary Hybrids will differ) offline electronic payments are not an issue. When the internet connection goes down a device can automatically detect it and roll over to a land line without user intervention or the payment system can store and forward, even with EMV chip payment terminals.

 With Acme Worry Free IT the internet can also be used for backup of point of sale (and other data like spreadsheets, documents and images) as well as remote support, remote access, monitoring, training etc. -In other words, you can get into your point of sale system and access all your programs (not just point of sale) from anywhere and any device.